This application claims the priority of German application 198 40 843.9, filed in Germany on Sep. 7, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a fan impeller assembly, in particular a fan impeller which can be used in the cooling system of internal combustion engines. Preferred embodiments of the present invention relate to a fan impeller assembly for cooling systems of internal combustion engines, comprising: a cup shaped hub, adjustable fan blades which are guided rotatably in a peripheral wall of the hub, and an actuating drive operable to adjust the fan blades and situated in the cup-shaped hub, said actuating drive including: an actuating element spring-loaded toward an initial position and acted upon in an opposite direction by a pressure medium, and adjusting eccentrics which are situated at a transition between said actuating element and the fan blades and can be acted upon by the actuating element, the actuating element being formed by a concentrically arranged actuating piston which adjoins the cup wall in a sealing manner and is guided by the latter.
In the case of a known fan impeller of the abovementioned type (DE-A 28 07 899) with a cup-shaped hub, the fan blades are mounted in the cup wall and, at an axial offset therefrom, the hub forms the holder and sealing guide for an actuating piston which can be loaded by means of pressure medium, is supported resiliently in the opposite direction and acts as an actuating element for the fan blades. The adjusting eccentrics assigned to the fan blades are formed by pivoting levers which extend in the circumferential direction, are connected to the fan blades in a rotationally rigid manner within the hub and are acted upon by means of axially extending actuating rods which are supported against the piston. Although a configuration of this kind allows relatively large piston diameters, the axial offset of the piston relative to the fan blades leads to a relatively large overall depth of the hub, even in the case of relatively small pivoting angles for the fan blades, and also involves relatively high outlay on construction.
Other known publications relating to the technical background are DE 88 15 383 U1, DE 84 06 829 U1, DE 25 52 529 A1 and DE 44 38 995 A1.
The invention relates to the configuration of a fan impeller of the type stated at the outset and has the object of arriving at a basic design of fan impeller which is of simple, small and flat construction and allows such a fan, the direction of delivery of which can be reversed while the direction of rotation remains the same, to be used in existing designs instead of conventional blower impellers. This object is achieved according to preferred embodiments of the invention by providing a fan impeller assembly of the type referred to above, wherein a piston wall of the actuating piston lies in radial overlap with the fan blades as an actuating ring for receiving actuating stubs of the adjusting eccentrics, and wherein, by a pressure medium acting on the actuating piston, the fan blades can be changed over into a direction of delivery opposite to a direction of delivery in an initial position and, in both of the opposite directions of delivery, are loaded in the directions of the blade position corresponding to the respective direction of delivery.
By virtue of the fact that an axially displaceable actuating piston is used, the operation of the actuating piston is independent of the respective speed and its surface area can be dimensioned in such a way, based in particular on the respective size of the hub, that sufficiently high actuating forces are obtained even at low actuating pressures. This configuration furthermore provides the possibility of creating sufficient space for an elastically flexible return device of simple configuration, with the result that, overall, an actuating device is created in which active adjustment takes place in each case in only one direction of actuation and in which the return is accomplished by means of the passive elastically flexible return device, which operates against the actuating force of the pressure-loaded actuating piston. This makes it possible to obtain an actuating device in which pressure loading is necessary in only one direction and the change-over can be accomplished by switching the pressure loading on and off. If a pump, a compressor, an accumulator or the like is provided for the purpose of pressure loading, there is thus no need for any further control devices but only for the pressure source to be switched on and off. With a view to as compact as possible an axial overall length, an axially overlapping arrangement of the actuating piston and the fan blades is of particular and independent significance.
Particularly in the case of pneumatic actuation, this leads to a very simple solution, making possible a basic concept such that the end position which is adopted by means of the elastically flexible return device corresponds to a normal working position of the fan impeller as the forward-blowing direction. There is therefore no need for any pressure supply in the normal working position, maximum reliability of operation is thus ensured and, moreover, a very energy-saving operation is made possible if, upon pressure loading, only a brief working position is adopted as the reverse blowing direction. This can be accomplished simply by switching on a pump or a compressor, especially as the large-area dimensioning allows operation at very low pressures.
Particularly in connection with pneumatic actuation of the actuating device, it is possible, if the source of compressed air is switched on only briefly to build up the required actuating pressure and then switched off, for the change-over from the reverse blowing position as the brief working position to the normal working position as the forward-blowing position to be achieved simply by carrying out the pressure reduction in a delayed or time-controlled manner.
This can be achieved in a particularly simple manner if the volume closed off by the actuating piston is connected, for example, to atmosphere by a restrictor opening, if required in a controlled manner.
By virtue of the fact that, in the case of the solution according to the invention, the fan blades are loaded in their respective end position by a holding force which is independent of the actuating device and acts in the direction of the end position, in particular by the force of the air resistance acting on the fan blades, it is possible, in conjunction with a time-controlled pressure reduction as explained above, to design the actuating device in such a way that a virtually immediate change-over between the two end positions is obtained, not only when changing over from the normal working position into the brief working position but also when changing over in the opposite direction. This is because, with such a configuration, the actuating force supplied by the elastically flexible return device can be dimensioned in such a way in relation to the self-holding force that it is only slightly greater than the self-holding force, allowing a virtually complete pressure reduction to be formed before the change-over takes place, the change-over then taking place abruptly since there is no significant opposing force being exerted by the actuating piston once the self-holding force has been overcome, due to the pressure reduction which has taken place. The use of the force of the air resistance acting on the fan blades as a holding force represents a particularly advantageous solution.
As regards the switching time, switching from the normal working position to the brief working position is essentially dependent only on the delivery capacity of the pressure source or a corresponding reservoir volume acting as a source of supply.
The configuration of a fan impeller with adjustable fan blades and with a holding force, as the self-holding force, in their respective end position which is independent of the actuating device and acts in the direction of the end position also proves essential as regards stabilization of the fan blades in their respective end position and hence for reliable operating behavior since, in this way, it is possible without additional expenditure to achieve a stable end position in which the blades do not flutter and the blades assume a virtually fixed position relative to the hub despite their adjustability. Moreover, this effect can be achieved without additional expenditure if, in accordance with the invention, the fan blades are loaded in the direction of the respective end position by the force of the air resistance acting upon them counter to the direction of delivery.
The construction of the eccentric mechanism with a common actuating ring formed by the cylindrical wall part of the actuating piston in conjunction with the radial orientation and mounting of the fan blades in the hub housing and the axial overlap with the actuating piston leads to a particularly simple and flat construction in accordance with the invention.
As seen radially from the outside, the fan blades are each curved in a direction opposite to the direction of delivery, resulting in section in a convex fan blade curvature counter to -the direction of delivery, that end of the respective blades which projects forwards in the direction of delivery having a predominantly axial orientation, and the rearward end relative to the direction of delivery having a largely radial orientation.
For the change-over between the directions of delivery, rotation of the blades about their respective centre line has been found to be expedient, more particularly at an angle of, preferably, more than 90.degree., in particular at an angle of the order of about 110.degree., it being possible to influence the magnitude of the self-holding force both by means of the shape of the blade profile and/or the angle of incidence and/or the axial distance of the respective blade edge at the front in the direction of delivery from the axis of rotation of the fan blade.
The basic concept according to the invention of a fan impeller with adjustable fan blades furthermore makes it possible as an optional additional function, while retaining the principle of construction and in accordance with the invention to perform speed- and/or temperature-dependent adaptation of the cooling performance in order to reduce the cooling performance, which, in principle, rises with the speed in the case of a predetermined rigid ratio between the speeds of the crank shaft and the fan impeller, if there is no need for such cooling performance. In the case of a fan impeller according to the invention, this is achieved by virtue of the fact that the spring-loaded initial position of the actuating piston is stop-limited counter to the spring force and the position of the limiting stop is varied as a function of the speed and/or temperature.
The starting point here is that, for a large number of applications, especially for machines such as agricultural and stationary machines and also commercial vehicles and utility vehicles and, in this context, especially agricultural utility vehicles such as tractors, the internal combustion engine is generally operated within a relatively narrow working range and there is thus no need for continuous adjustment of the fan blades. The working range mentioned is generally a range in which the internal combustion engine is below its maximum speed and in which the cooling performance requirement is high, in particular at a maximum, based on the maximum torque that can be achieved in this range or maximum power that can be achieved in this range. Starting from this range, the air delivery rate and cooling performance that can be achieved thereby generally increases more steeply with increasing speed than the respective maximum cooling performance requirement. This can be allowed for by the configuration according to the invention by adjusting the angle of incidence of the fan blades--so as to reduce the cooling performance--in the direction of a lower air delivery rate, and this can be accomplished directly as a function of the speed.
Such speed-dependent adjustment can be achieved--as an independent inventive solution--by means of the actuating force resulting from the force acting on the fan blades as a function of the air resistance, this force increasing with speed with the result that, based on the maximum cooling performance requirement for the working range mentioned, it is possible to perform adjustment where the air-resistance-dependent actuating force is in equilibrium with an elastically flexible support. If this working range is exceeded, i.e. if the speed is increased further, a correspondingly higher air-resistance-dependent actuating force is obtained in line with the increased speed, and the fan blades are pivoted to a smaller angle of incidence against the elastic support, it being expedient to delimit the permissible minimum angle of incidence by means of a fixed stop.
Within the context of the invention but also as an independently inventive solution, a corresponding adaptation can also be achieved as a function of temperature. This is possible by virtue of the fact that a stop element operating in a temperature-dependent manner is configured in such a way that a maximum deflection is obtained when the internal combustion engine is operating at a corresponding speed in the working range mentioned of maximum loading and maximum cooling performance requirement. If the speed goes beyond this, the rise in the cooling performance requirement lags behind the rise in speed, with the result that the temperature falls as a consequence of the increase in the air delivery rate and cooling performance against speed, this leading to a reduction in the deflection of the stop element which operates in a temperature-dependent manner and an adjustment of the fan blades in the direction of a smaller angle of incidence and a correspondingly lower air delivery rate by means of the air-resistance-dependent actuating force loading them.
According to the invention, this provides a solution which operates in a speed- and/or temperature-dependent manner and by means of which the power requirement of the fan impeller is reduced in the critical upper speed ranges to the level required to cool the internal combustion engine, thus reducing the power losses of the internal combustion engine, with correspondingly positive effects on the effectively available power of the internal combustion engine and on fuel consumption.
The temperature-dependent adjustability according to the invention, if required in combined form to give temperature- and speed-dependent adjustability, furthermore provides the assurance that there will be no deficit in cooling performance in the case of a higher cooling performance requirement in the speed range above said working range since, given an elevated temperature and a corresponding retroactive effect on the temperature-dependently operating stop element, the angle of incidence of the fan blades even in the speed range above, i.e. beyond, the working range mentioned can be adjusted or can be set to an angle of incidence which corresponds to the maximum delivery rate if the temperature-dependently operating stop element is designed in such a way that it can also withstand higher air-resistance-dependent actuating forces occurring as a function of the speed.
Springs, in particular helical springs, can be used as elastic stop elements, and expandable-material elements, in particular, can be used as temperature-dependent stop elements.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.